Compensatory Evolution of pbp Mutations Restores the Fitness Cost Imposed by β-Lactam Resistance in Streptococcus pneumoniae
Figure 2
Effect of pbp mutations on cell morphology.
Cells were prepared for microscopy and stained with DAPI as described in Materials and Methods (bar scale, 5 µm). (A) Merged phase-contrast and DAPI fluorescence image of the pbp mutants showing a bacillar morphology, contrasting with the typical coccoid shape of the CP1015 (wt) strain. (B) Cell shape modifications of the cell populations detected by flow cytometry analysis. Exponentially growing bacterial cells were injected into a flow cytometer and the results were analyzed with the WinMDI software. To compare populations, the data for each strain were plotted on a two-dimensional graph (x-axis, forward scatter; y-axis, side scatter).